Cardiac arrest (CA) and stroke remain two of the leading causes of death and disability in the U.S.A. In particular, CA with its consequent disruption of blood flow sets in motion a cascade of cellular derangements that result in selective brain damage and delayed cell death. It has been postulated that delayed cell death after brain ischemia may result from two different mechanisms: apoptosis and/or necrosis. In both pathways however, mitochondrial dysfunction appears to play a pivotal role. However, the precise mechanisms of how mitochondrial dysfunction occurs following cerebral ischemia have not been fully elucidated. Although different signaling pathways are expected to play a role in mitochondrial dysfunction, our main hypothesis is that an aberrant signal transduction pathway involving protein kinase C delta (dPKC), underlies mitochondrial dysfunction (Figure 1). In contrast to the negative role of dPKC, we have recently demonstrated that ePKC plays a pivotal role in the induction of tolerance after ischemic preconditioning (IPC). In contrast to the pro-apoptotic role of dPKC, cleavage of ePKC by caspase-7 results in the activation of ePKC, which was associated with its anti-apoptotic function in MCF-7 cells. Cleavage of ePKC has never been reported in the CNS. Also, formation of mitochondrial ePKC-ERK 1/2 modules was coupled to the inactivation of Bad, a pro-apoptotic molecule. Since ischemic preconditioning has been shown to preserve mitochondrial function, we conjecture that ePKC promotes ischemic tolerance by protecting mitochondrial function. We propose in this application to determine the mechanisms by which ePKC protects neuronal mitochondria whereas dPKC promotes cell death after cerebral ischemia. To this end, we propose the following aims: 1) Determine the mechanisms and time course that promote translocation/activation of either ePKC or dPKC in neurons after IPC/ischemia or pharmacological stimuli and whether these isozymes translocate to mitochondria;2) To determine the mechanisms by which dPKC translocation/cleavage promote mitochondrial dysfunction and their role in neuronal death after cerebral ischemia;and 3) To determine the mechanisms by which ePKC translocation/cleavage promote mitochondrial protection after cerebral ischemia.